The worst scenario based on an asteroid 1 kilometer wide would re-create the hole in the ozone layer, which appeared over Antarctica during the 1990s, except this would be worldwide. UV levels in the study's simulation soared beyond anything measured so far on Earth by the UV Index's daily forecasts of overexposure to UV radiation, and remained that way for as long as two years.
Researchers tested scenarios with a 0.6-mile asteroid and a 0.3-mile asteroid (500 meters) at a specific location and specific time of year. Models used in the research showed how ozone destruction would result from an asteroid strike launching seawater vapor hundreds of miles up into the highest parts of the atmosphere. Chemical elements such as chloride and bromide that separated from the water vapor could then wreak havoc by destroying the ozone layer that protects life on Earth from UV rays.
Long-term effects of such high UV radiation would include skin-reddening, changes in plant growth and genetic mutations for humans and other organisms. And an asteroid has about twice the chance of striking water rather than hitting land. Those odds come from the fact that over 70 percent of the Earth's surface is covered by water.
Asteroid hunters have found about 903 of an estimated 1,050 near-Earth objects (NEOs) with diameters of 1 kilometer or greater as of October 1. That still leaves well over 100 objects in the 1-2 kilometer size undiscovered.